Air-Borne Ultrasonic Transducers Based on Cross-Linked Polypropylene Ferro/Piezoelectrets

Abstract

Air-borne ultrasonic transducers based on irradiated cross-linked polypropylene (IXPP) ferro/piezoelectret films, which exhibit a high longitudinal piezoelectric activity and a low acoustic impedance, were analyzed, fabricated, and measured in this work. Equivalent circuits and finite element models for IXPP film transducers were built to predict and confirm the transducer performances. Circular IXPP transducers which are 20 mm in diameter show a maximum radiated pressure of 3.2 Pa (104 dB) driven by 100 Vrms and a receiving sensitivity of 8 mV/Pa when resonance occurs at around 45 kHz, both at a distance of 60 cm, as confirmed by analytical and numerical models. Pulse-echo response of the transducers was obtained from theoretical calculation and simulation as well, indicating a −6 dB bandwidth of around 25% is achieved. Besides, the directivity patterns of IXPP film transducers at various frequencies were measured and analyzed. This work may introduce a novel material for flexible ultrasonic transducers with a demand of high sensitivity.